Today, many items that used to be made of wood are made of extruded cellular plastic materials such as general purpose or crystalline polystyrene extruded with a blowing agent. These materials are light, inexpensive, and relatively strong for their density. Examples of items that sometimes are formed of such cellular plastic panels include cornice boards, crown mold, point of purchase displays, baseboard molding, and the like. In many instances, such as in forming cornice boards and point of purchase displays, cellular panels must be attached together at their ends to form a box-shaped article. In the past, attaching extruded cellular panels together at their ends has given rise to numerous problems in the extrusion industry. Since the cellular plastic material is relatively light and porous, it cannot be attached with fasteners such as screws or nails. In addition, extruding the panels with slots or channels to accept corner keys, attaching brackets, or other fasteners has not been practical because the stress imparted by the fastener to the cellular plastic can easily break the channels under even slight stress allowing the structure to come apart.
Usually, cellular panel extruders have been left only with the option of gluing panels together at their corners with specialized glues to form box or other shaped articles. This process is time consuming, inefficient, and usually requires that the structure be assembled at the manufacturer's location, since the gluing process requires special glue, clamps, and expertise. It would be highly desirable to be able to attach extruded cellular thermoplastic panels together at their ends easily and without glue so that they could be shipped disassembled and assembled into box or other shapes on site by the end user.
Some attempts have been made to provide efficient reliable methods of attaching cellular plastic panels together at their ends. For example, U.S. Pat. No. 5,348,778 of Knipp et al. discloses sandwiching a cellular polyurethane core between rigid panels that form a shell. Flexible polyurethane edge profiles are then fixed along the panel edges between protruding ends of the shell. These profiles are formed to mate together with profiles of like panels to define a water tight joint between the panels. While this method is an improvement in attaching panels together end to end, it is not well suited to attaching panels to form box shapes. In addition, forming the sandwiched shell panels and attaching the flexible end pieces is a multi-step process that is inefficient and time consuming. Thus, the disclosure of Knipp et al, is not a viable option for attaching cellular plastic panels together to define box shapes such as those used in point of purchase displays, cornice boards, and the like.
U.S. Pat. Nos. 4,164,526 of Clay et al., U.S. Pat. No. 4,157,413 of Ruhl, U.S. Pat. No. 4,154,784 of Ruhl, U.S. Pat. No. 4,028,450 of Gould, U.S. Pat. No. 4,001,361 of Unruh, and U.S. Pat. No. 3,815,657 of Malek et al. all concern cellular plastic panels and junctions therebetween. However, none of these patents address the problem of efficient on-site attaching of such panels together at their ends to form box or other shaped articles.
Accordingly, there exists a need for an extruded cellular plastic panel with provisions for attaching the panel to like panels at the ends of the panels to form box or other shapes. Such a panel should be easily extruded, should require no retrofitting of components such as surface shells or end profiles, and should be able to be assembled by the end user quickly, easily, and reliably. It is to the provision of such an extruded cellular panel and to a method of fabricating the panel that the present invention is primarily directed.